Method and composition to divert fluids at high temperatures

ABSTRACT

Methods of treating a subterranean formation as a portion of steam-assisted gravity drainage operation including providing a fluid containing a diverting agent, injecting the fluid into a first wellbore, allowing the diverting agent to divert fluid placement, performing steam-assisted gravity drainage, and producing formation fluids from a second wellbore.

RELATED PATENT APPLICATION INFORMATION

This patent application claims priority to and the benefit ofprovisional patent application U.S. 61/383,590, filed Sep. 16, 2010,which is incorporated in its entirety herein.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Various thermal methods have been proposed for the production of heavyoils. Variation of steam flooding (direct steam flooding, cyclic steamstimulation, etc) and steam-assisted gravity drainage (SAGD); see U.S.Pat. No. 4,344,485, incorporated herein, are the two most commonmethods. Of the two, steam flooding has been tested in the field and hasbeen commercially used. However, SAGD has been only recently becomecommercialized. With better understanding of the SAGD process and morefield experience, this particular method has gained considerableattention recently. Currently, there are several producing wells usingSAGD process and more than twenty five (Strategy West Inc., 2006;Alberta Economic Development, 2006, incorporated herein) SAGD projectswhich are under construction or approved to be online in the next decadein Canada alone. The total investments on SAGD projects alone so farexceeds 12 billion dollars (Strategy West Inc.—Alberta EconomicDevelopment, 2006, National Energy board, 2006, incorporated herein).

One challenge in using SAGD for heavy oil production is even heating ofthe formation and associated fluid. This challenge is relevant to boththe start-up phase of the SAGD process where proper thermal &hydrodynamic communication is being established between the horizontalwell pairs as well as the production phase where steam is being used todeliver heat to the reservoir, thus lowering the viscosity so that theheavy oil can be produced by gravity drainage. It has also been observedin the field that heating of the well pairs and the reservoir itself isoften not uniform due to variations if fluid and reservoir propertiesthat can lead to “blind” areas where there is no contact with steam. Inthe start-up phase, the influence of geology of the reservoir, SAGD wellpair completion design, well pair operating conditions, and many otherfactors leads to long periods (up to 4-6 months) before the thermal andhydrodynamic communication between the well pairs is suitable enough foractual production. Even then, there may be regions along the length ofthe horizontal length that communications are not uniform. During theproduction phase of a SAGD operation, non-uniform injection of steam tothe reservoir for the purpose of oil production is likely affectingoverall efficiency of the steam injection process and the ultimaterecovery. The non-uniform injection of steam and uneven steam sweepcould be seen both in a SAGD well pair arrangement and in a traditionalsteam flooding (either continuous or cyclic) methods.

It is expected that reducing the required time for uniform well paircommunication and uniform distribution of steam injection duringproduction phase will drastically affect the economics of the any steamassisted heavy oil production project.

SUMMARY

In a first aspect, methods of treating a subterranean formation as aportion of steam-assisted gravity drainage operation are provided whichinclude providing a fluid including fibers or other diverting agent,injecting the fluid into a first wellbore, allowing the fibers or otherdiverting agent to function as a diverting agent, performingsteam-assisted gravity drainage, and producing formation fluids from asecond wellbore.

In a second aspect, methods of treating a subterranean formation as aportion of steam-assisted operation, include providing a fluidcomprising fibers or other diverting agent, injecting the fluid into afirst wellbore, allowing the fibers or other diverting agent to functionas a diverting agent, and performing steam-assisted production offormation fluids from a second wellbore.

Some other aspects are methods of treating a subterranean formationincluding providing a fluid comprising a diverting agent and adhesive,injecting the fluid into a first wellbore, allowing the diverting agentto divert fluid placement, and performing steam involved production offormation fluids from a second wellbore.

Some embodiments of this invention provide a composition, method andprocess to optimize the production and stimulation of SAGD well pairswith fluids that contain solid state diverting agents—fibers inparticular. In particular, we use composition, method and processesthat:

-   1) Selectively plug or block a high permeability zone during steam    injection for the purpose of heavy oil production i.e. either during    start up or production phase, in order to evenly distribute the flow    of steam to the formation.-   2) Plug naturally occurring or steam induced fractures in the    formation. Fibers are very effective at this.-   3) As a plastering agent to cover the surface of a high permeability    region of the wellbore.-   4) As a plug, plaster, film or fabric forming particulate agent that    selectively plugs screens or ports on the liner in the steam    injection wellbore. The ports and particulate agent can be    co-designed to work together similar to a lock and key. That is,    some particles can block off some ports but not others.-   5) As a temporary plug in the wellbore (i.e. you form a temporary    bridge plug).-   6) As a diverting agent in stimulation and workover treatments on    SAGD wells—both on the steam injector well, and on the producing    well. to allow the removal of scale from the production tubulars.

The artificial plug can be designed to be long lived or it can bedesigned to collapse or degrade, possibly over a short period of time,to open up the high permeability zones for complete steam sweep duringproduction. The objectives are achieved by:

-   Identifying low permeability/low fluid mobility areas (zones) or    equally high permeability/high fluid mobility areas (zones) around    the injector and producer wells through appropriate downhole tools.-   Temporarily plug a specified part of the formation by the high    temperature fiber composition by either active or passive placement    methods.

DESCRIPTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation—specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein can also comprise some components other than thosecited. In the summary of the invention and this detailed description,each numerical value should be read once as modified by the term “about”(unless already expressly so modified), and then read again as not somodified unless otherwise indicated in context. Also, in the summary ofthe invention and this detailed description, it should be understoodthat a concentration range listed or described as being useful,suitable, or the like, is intended that any and every concentrationwithin the range, including the end points, is to be considered ashaving been stated. For example, “a range of from 1 to 10” is to be readas indicating each and every possible number along the continuum betweenabout 1 and about 10. Thus, even if specific data points within therange, or even no data points within the range, are explicitlyidentified or refer to only a few specific, it is to be understood thatinventors appreciate and understand that any and all data points withinthe range are to be considered to have been specified, and thatinventors possessed knowledge of the entire range and all points withinthe range.

Stimulation and remediation of SAGD well pairs (both injector andproducer) requires novel fluid diversion technologies as well. Cracksand high permeability streaks will form in the formation during SAGDproduction, and can act as thief zones for scale inhibitors, acidizingand other workover fluids during remediation treatments. However, oftenthe productive formation (steam affected region) is still at very hightemperatures (in excess of 300-400° F.). High temperature may alsoinclude any temperature point in the range from about 200° F. to about500° F. It is possible there is a strong economical incentive tointervene in the SAGD completion at as high as temperature as possible.By intervening at high temperatures: 1) it takes less time to cool down,2) less of the energy spent to heat up the formation is lost, 3) theviscosity of the bitumen is lower—facilitating displacement and surfacereactions, and 4) the intervention occurs at a physical and chemicalenvironment that is closer to operation conditions (less thermal cyclingof the rock).

Although fluid diversion techniques including viscous pills,self-diverting acids, and viscoelastic diverting acids (VDA) have beenpractices in conventional reservoirs, they may not be reliable at thesehigh temperatures. Solid state diverting agents are thus required, butmany of the traditional additives, such as benzoic acid flakes, rocksalt, and the like, may not be practical at these high temperatures.Benzoic acid melts at 122.4° C., and rock salt can cause corrosionissues on expensive wellbore completion tubing, screens and hardware.

Methods to speed up communications in SAGD well pair arrangement areproposed. The majority of these inventions and proposed methods arebased on heating the reservoir matrix between the two horizontal wellpairs, and thus reducing the viscosity of the heavy oil trapped betweenthe two wells and mobilizing it to the producer well. A common method issteam circulation in the well pair. One of the main difficulties duringthe steam circulation and production phase is even distribution ofsteam. Blocking of the thief zones (zones with high permeability) may beused as a method to target the low permeability zone in the early stagesof steam injection. High permeability blocking methods have beentraditionally used to divert formation treatment fluids to desiredlocation—but as discussed above they are not particularly useful forSAGD interventions. One of the main challenges in applying the samemethodology in a steam injection scenario is the capability oftraditional methods to withstand very high temperatures experienced insteam injection heavy oil production methods.

In well stimulation industry, mechanical and chemical methods can beused to divert fluids to the desired zones. Mechanical methods tend tobe more expensive and time consuming and their implementation requiresmultiple phases. The chemical methods can involve either injection ofparticulate laden fluids to form an impervious cake around the wellboreor using foaming, emulsifying, or gelling agents (fluids) toartificially reduce the permeability of the targeted zone and thusdivert the flow of stimulation fluids. In one method, formationtreatment fluid (FTF) plus fiber is used to selectively plug an area ofthe formation.

The chemistry of some compositions used in embodiments aredeveloped/designed in such a way that artificial chemical block canwithstand the very high temperature of steam injection processes (i.e.temperatures as high as 300° C.) in a timely fashion. The divertingagent or bridging material can be of a non-fibrous or fibrous material(in the following paragraphs the terms “fiber”, “bridging agent”, and“diverting agent” may all refer to the same material). The chemistry ofthe composition, and the physical structure of the fiber, can bemodified in such a way that the plug integrity can be maintained over acertain period of time (up to few weeks or few months) under steaminjection conditions. This can be controlled by selecting theappropriate fibrous or particulate material for the task. If a plug isto last a very long time, then a hydrolytically stable fiber such asKYNOL (Novoloid Resin) can be used. If the plug is to last a short time,then glass fibers of different grades can be used. In general glassfibers with alkali resistant (commonly referred to as AR glass)compositions have longer lifetimes at higher temperatures than the morecommon E-glass. If the plug is to last a very short time then hightemperature polyesters or other condensation polymers can be used. Theinvention also includes aspects of making the diverting agents withphysical properties that facilitate transport at the low velocities ofsteam injection. The particulate could contain glass bubbles to reducethe density. They could also have high surface areas to facilitateentrainment in the steam.

The physical structure of the fiber, particularly its diameter and itssurface to volume ratio may have an impact on the dissolution anddegradation of the material. Fibers that have a high surface area tovolume ratio may tend to degrade faster. Degradation can also bemodified by physical and chemical methods that modify the diffusion rateof water molecules in the material. For example polymers can beelectron-beam crosslinked to increase their melting temperatures anddecrease their permeability.

In some embodiments, the term “fibers” may refer to any particulatematerial with an aspect ratio. Therefore the fiber could be a ribbon,strip or plate.

In one embodiment, the composition and method may be used to plaster orcoat a portion of the wellbore. This method may utilize an adhesivebinder. In such case, placement and performance of the fibers and theperformance of the resultant fiber plugs can be assisted by the use ofpermanent or temporary adhesive materials. These materials can be heatand or hydrolytically activated. One method would be to use fibers wherethe adhesive is an integral component of the material. Adhesiveplacement could be useful for creating “spray-on” active barrier plugs.

To achieve some embodiments of the invention, placement method can beconsidered. The composition may be placed by either active or passiveplacement methods. In active placement method, method and compositionwill be preferentially placed by using a coiled tubing arrangement. Thisapproach provides the mean to intervene during the ongoing production,in an effort to correct or improve the liquids and steam flow.

In passive placement approach, the fiber containing fluid could beco-injected with the steam, thereby not requiring a significantintervention at the wellhead. In such a case, the composition will becarried with the carrier fluid and most likely will end up in highpermeability areas where majority of flow to the subterranean formationoccurs. Passive placement could be achieved by any suitable method. Asone example, if the steam flux is high enough it could be achieved bymetering in fibers at a very low concentration. The fibers wouldaccumulate at the regions where the most steam is being injected.Alternatively the fibers could be mixed into a high temperature emulsionor fluid and bullheaded into the well. Alternatively various methods ofviscosifying the steam, such as the use of foaming agents could be used.

A potential concern for passive placement of the fibers is thesettlement of the fibers from the carrier fluid during transportation tothe placement location. As such, the type of carrier fluid and the flowregime in the wellbore tubing may help achieve fiber placement in thewell. A turbulent all-steam stream may be used to carry the fibersdirectly to the placement position carrying the fibers similar toaerosol. Potentially an all-liquid stream possibly even in a laminarflow regime may also be able to carry the fibers to the placementlocation. Depending on the nature of fibers, a compatible aqueous ornon-aqueous liquid may be used. It is expected that a laminar two phase(gas-liquid) will be least efficient flow regime for fibertransportation as most likely they will settle particularly underlaminar flow regime. However, a two-phase slugging flow may be effectiveat placing particulate material as a plug.

Another aspect is the active design and selection process so that thebridging material, and the particular port or screen used in the linerof the injection well work together in concert to achieve the desiredeffect. We have a composition, method and process to:

-   1) To selectively plug or block a high permeability zone during    steam injection for the purpose of heavy oil production i.e. either    during start up or production phase, in order to evenly distribute    the flow of steam to the formation.-   2) As a method to plug naturally occurring or steam induced    fractures in the formation; fibers are may be effective for such.-   3) As a plastering agent to cover the surface of a high permeability    region of the wellbore.-   4) As a plug, plaster, film or fabric forming particulate agent that    selectively plugs screens, slotted liners or ports on the liner in    the steam injection wellbore. The ports and particulate agent can be    co-designed to work together similar to a lock and key. That is,    some particles can block off some ports but not others.-   5) As a temporary plug in the wellbore (i.e. form a temporary bridge    plug).-   6) As a high temperature diverting agent for stimulation, workovers    and interventions into both the injector and production well.-   7) As a diverting agent to allow the removal of scale from the    production tubulars.

Situations 1-3 may have the particulate material pass through thehardware and liner of the injector well into the formation. When this isthe desired effect, such as the case of geological situations wherethermal fracturing of the formation is likely, then the artisan maychoose a liner/bridging material combination where the bridging materialis forced into the formation. The geometry of the screen or slot couldbe designed to facilitate this process, and the bridging material can bedesigned to penetrate this aperture.

Another consideration regarding the application of fibers is theiraspect ratio with respect to slot sizes in the slotted liner of the wellcompletion. In some cases, the smallest recommended slot width is about150 microns. Additionally, the slot design is an important factoraffecting anti-plugging characteristics of the slots. The other factorthat may also affect the flow of fibers is that the slot design(configuration) may be different for the injection and production wells.

Situations 4 and 5 require the particulate material to bridge out in theinjector wellbore or on the ports, screens or slots that provide accessto the well bore. In such situations, the artisan may want to size thebridging material so that it would collect on the screen or port.

Another aspect in some embodiments is the method of feeding the bridgingmaterial into the injection well.

-   1. Slug: This could be a method of placing a diverting agent that is    of a permanent nature. Also if plugging a thermal fracture from a    producer well side is desired, then the placement of this plug may    be via a slug approach.-   2. Continuous: This could be an option for uniform placement of    steam if a light-weight degradable fiber is used at low    concentrations. Since the fiber is entrained in the steam, the    greatest amount of fiber will follow the steam into high    conductivity channels—eventually plugging them and diverting the    steam to other locations along. If the fiber is chosen to degrade    slowly, then these plugs will not be permanent. Therefore, over time    the steam will be diverted back and forth through the formation such    as a river passing through a delta. The instantaneous effect would    not be one of uniform passage of steam through the formation, but    the time averaged effect would be.-   3. Semi-continuous: A combination of the above two approaches. This    may be the best for degradable materials that have a relatively long    lifetime, but are not permanent.

Another aspect of is an integrated junk basket, chamber, compartment, ormechanism to collect waste bridging material that may not be completelyplaced where intended, and to facilitate its degradation or periodicremoval. For example, an extended compartment could be placed at the endof the injector well (i.e. an intentionally designed rat hole).Alternatively, a tubing could be placed in the Steam Injector line sothat compressed gas, foam, or another fluid could be blown backwards toclear out the debris. Alternatively a capillary line could be placed tospot reactive material (such as an acid) on waste bridging materialdebris to enhance degradation.

While the invention has been shown in only some of its forms, it shouldbe apparent to those skilled in the art that it is not so limited, butis susceptible to various changes and modifications without departingfrom the scope of the invention. Accordingly, it is appropriate that theappended claims be construed broadly and in a manner consistent with thescope of the invention.

1. A method of treating a subterranean formation as a portion ofsteam-assisted gravity drainage operation, the method comprising: a.providing a fluid comprising a diverting agent; b. injecting the fluidinto a first wellbore; c. allowing the diverting agent to divert fluidplacement; d. performing steam-assisted gravity drainage; and, e.producing formation fluids from a second wellbore.
 2. The method ofclaim 1 wherein the diverting agent is functional at high temperature.3. The method of claim 1 wherein the fluid further comprises aparticulate.
 4. The method of claim 3 wherein the particulate furthercomprises glass bubbles to reduce the density.
 5. The method of claim 3wherein the particulate has a high surface areas to facilitateentrainment in steam.
 6. The method of claim 1 wherein the divertingagent is a fibrous material.
 7. The method of claim 1 wherein thediverting agent is a nonfibrous material.
 8. The method of claim 1wherein the diverting agent is a fibrous bridging agent.
 9. The methodof claim 1 wherein the diverting agent is a nonfibrous bridging agent.10. The method of claim 1 further comprising utilization of an adhesivebinder.
 11. The method of claim 10 wherein the adhesive binder is apermanent adhesive.
 12. The method of claim 10 wherein the adhesivebinder is a temporary adhesive.
 13. The method of claim 1 wherein thediverting agent is placed by an active placement method.
 14. The methodof claim 1 wherein the diverting agent is placed by a passive placementmethod.
 15. A method of treating a subterranean formation as a portionof steam-assisted operation, the method comprising: a. providing a fluidcomprising a diverting agent; b. injecting the fluid into a firstwellbore; c. allowing the diverting agent to divert fluid placement;and, d. performing steam-assisted production of formation fluids from asecond wellbore.
 16. The method of claim 15 wherein the diverting agentis functional at high temperature.
 17. The method of claim 15 whereinthe fluid further comprises a particulate.
 18. The method of claim 17wherein the particulate further comprises glass bubbles to reduce thedensity.
 19. The method of claim 17 wherein the particulate has a highsurface areas to facilitate entrainment in steam.
 20. The method ofclaim 15 wherein the diverting agent is a fibrous material or nonfibrousmaterial.
 21. The method of claim 15 further comprising utilization ofan adhesive binder, wherein the adhesive binder is either a permanentadhesive or temporary adhesive.
 22. The method of claim 15 wherein thediverting agent is placed by an active placement method or a passiveplacement method.
 23. A method of treating a subterranean formationcomprising: a. providing a fluid comprising a diverting agent andadhesive; b. injecting the fluid into a first wellbore; c. allowing thediverting agent to divert fluid placement; and, d. performingsteam-assisted production of formation fluids from a second wellbore.